The present invention relates generally to laser systems and, more particularly, to a system for transmitting a high-power laser beam onto a workpiece for welding, cutting or other processing of the workpiece with an unfocused laser beam.
High-power, such as 2000 Watt average power, lasers have a wide variety of applications, such as precision drilling, cutting and welding of metal workpieces. Neodymium:Yttrium-aluminum-garnet (Nd:YAG) lasers are particularly useful for such purposes. The beam generated by a laser, such as a Nd:YAG laser, must be transmitted to a work station where the beam is directed onto the material of the workpiece. In the prior art, system comprising an assembly of mirrors, lenses and prisms is used to transmit the laser beam to the work station. While this type of arrangement functioned satisfactorily in some applications, such a system is bulky and the flexibility with which the beam may be maneuvered about the workpiece is limited.
Conventional focused welding techniques are known, such as an electron beam welding system which utilizes a gun which focuses an electron stream by manipulating a magnetic focus coil, or in the case of a laser which utilizes a focusing head or output coupler that comprises a series of lenses and mirrors for receiving an emerging laser beam from an end of a fiber optic cable and delivering and focusing such laser beam to a desired spot on the workpiece. A typical laser welding system uses at least one mirror to reflect the laser beam into the lens and at least one lens to focus the laser beam onto the workpiece.
However, in many instances the workpiece is accessible only through narrow openings. The size of the focusing head may prevent it from accessing the workpiece through the opening. This requires disassembling the components of the workpiece in order to perform the operation or prevents access altogether (cannot be welded).
Moreover, when a weld is made through a narrow opening, the resulting large beam diameter impinges on the sides of the opening. Further, the reach of the beam is limited and may only be to one half of a joint's length and thus requires that the weld be made with two passages-one from each side of the joint. Welding half of the joint at a time results in overlapping of the weld at the center and launching the beam from outside the narrow opening may cause impingement melting on the top of the opening.